Storcli: show the physical drives health information

For now only temperature and SSD life left are supported.
[tests] Test Storcli.virtual_drives with non-trivial raid_type

Also a negative test checking the error path (the specified
command does not exist).
[tests] Refactor unit tests

Mocking the whole subprocess module is not such a bright idea
(for one there's no point in mocking exceptions)
[test] Check if the non-zero exit code of storcli is handled properly
[test] Storcli.controller_details: check controller_id == None handling
[tests] Added unit tests for various utility functions